Jurgen Klopp admits Joe Gomez could require surgery to repair his leg fracture in what could be a substantial blow to Liverpool's Premier League title challenge.
Defender Gomez was initially expected to be sidelined for up to six weeks after sustaining the injury to his lower left leg in the Reds' 3-1 win at Burnley on December 5.
However, the England international is yet to resume training and is expected at least to miss the first leg of the Champions League last-16 tie with Bayern Munich on February 19.
And Klopp fears an operation could be needed to help Gomez's recovery, telling reporters: "We will see. It is possible, probably.
"It is not exactly going how we want. That's how it is. He needs more time. We will see exactly how we do it.
"There were different moments when we thought we could do this or that. It will take time. We cannot say more."
Liverpool are also without centre-back Dejan Lovren for Monday's trip to West Ham, with the Croatia international struggling with a hamstring problem.
James Milner is expected to play at right-back at London Stadium in the absence of Gomez and Trent Alexander-Arnold, who is recovering from a knee injury.
Liverpool are five points clear at the top of the table after 24 matches.
